# I need help understanding this circuit

Discussion in 'The Projects Forum' started by sirmax, May 6, 2011.

1. ### sirmax Thread Starter New Member

Apr 3, 2010
8
0
I am trying to figure out the Purpose of every object in this circut.
Those are my thoughts on most of them so far....

when a signal comes in the mic the 10kΩ resistor provides the correct current to the mic (0,9mA).
resistors R2,R3, and R6 are to prevent any loss of the AC signal going to the Amp.
comparitors C1 and C3 prevent the DC current going to the Amp.
comparitors C2 and C4 are so only the positive signal gets amplified.
because of the R4 and R5 resistors the amplification is times x100.
R8 so the leds get a right currrent.

what is the use of R7 in this curcuit and the diode ??

i am probably wrong somewhere in explaining this but i am trying to learn how all this works.
Hopefully some genius out there can take a little time to look at this and share his thought with me.
any help will be highly appretiated.
Thank you.

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2. ### Audioguru Expert

Dec 20, 2007
11,180
1,323
Only if the mic is shorted. The mic draws about 0.5mA so it has 4V across itself.

No.
R2 and R3 bias the input of the opamp IC1/1 at half the supply voltage so it can be a good amplifier.
R6 sets the input of opamp IC1/2 at 0V.

There are no comparators. C is capacitor.
The coupling capacitors C1, C2 and C3 couple the audio but block the DC.

No.
The gain of the first opamp is exactly 101 because it is non-inverting. Its gain is 100 if it is inverting.

Yes.

The circuit is wrong because loud sounds cause the input of opamp IC1/2 to go more negative than the max allowed voltage of only -0.3V. So C3 should not be used. Instead the opamps should be DC-coupled and the reference for IC1/2 should be biased at half the supply voltage so it matches the idle output voltage from IC1/1.

They make a peak detector where opamp IC1/2 quickly charges capacitor C4 through the diode then the capacitor is slowly discharged by R7 while the diode blocks the output of IC1/2 from discharging the capacitor quickly.
The peak detector probably allows only sounds that repeat fairly slowly from clocking the CD4017 sequencer.

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3. ### sirmax Thread Starter New Member

Apr 3, 2010
8
0
Thank you so much for taking the time to explain this to me
I really love this forum !
Highly appreciated my man

4. ### kaiosama New Member

Dec 6, 2010
29
0
Audioguru, how do you know all this ??????? Are we supposed to learn that in EE school?

5. ### Audioguru Expert

Dec 20, 2007
11,180
1,323
I learned the basics in university then learned the details from experienced engineers on the job and working on my own.
I also learned a lot on these forums. You can too.

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